/*
 * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.lang.model.type;

/**
 * A visitor of types, in the style of the visitor design pattern. Classes
 * implementing this interface are used to operate on a type when the kind of
 * type is unknown at compile time. When a visitor is passed to a type's
 * {@link TypeMirror#accept accept} method, the <tt>visit<i>XYZ</i></tt> method
 * most applicable to that type is invoked.
 * 
 * <p>
 * Classes implementing this interface may or may not throw a
 * {@code NullPointerException} if the additional parameter {@code p} is
 * {@code null}; see documentation of the implementing class for details.
 * 
 * <p>
 * <b>WARNING:</b> It is possible that methods will be added to this interface
 * to accommodate new, currently unknown, language structures added to future
 * versions of the Java&trade; programming language. Therefore, visitor classes
 * directly implementing this interface may be source incompatible with future
 * versions of the platform. To avoid this source incompatibility, visitor
 * implementations are encouraged to instead extend the appropriate abstract
 * visitor class that implements this interface. However, an API should
 * generally use this visitor interface as the type for parameters, return type,
 * etc. rather than one of the abstract classes.
 * 
 * @param <R>
 *            the return type of this visitor's methods. Use {@link Void} for
 *            visitors that do not need to return results.
 * @param <P>
 *            the type of the additional parameter to this visitor's methods.
 *            Use {@code Void} for visitors that do not need an additional
 *            parameter.
 * 
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @since 1.6
 */
public interface TypeVisitor<R, P> {
	/**
	 * Visits a type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visit(TypeMirror t, P p);

	/**
	 * A convenience method equivalent to {@code v.visit(t, null)}.
	 * 
	 * @param t
	 *            the element to visit
	 * @return a visitor-specified result
	 */
	R visit(TypeMirror t);

	/**
	 * Visits a primitive type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitPrimitive(PrimitiveType t, P p);

	/**
	 * Visits the null type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitNull(NullType t, P p);

	/**
	 * Visits an array type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitArray(ArrayType t, P p);

	/**
	 * Visits a declared type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitDeclared(DeclaredType t, P p);

	/**
	 * Visits an error type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitError(ErrorType t, P p);

	/**
	 * Visits a type variable.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitTypeVariable(TypeVariable t, P p);

	/**
	 * Visits a wildcard type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitWildcard(WildcardType t, P p);

	/**
	 * Visits an executable type.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitExecutable(ExecutableType t, P p);

	/**
	 * Visits a {@link NoType} instance.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 */
	R visitNoType(NoType t, P p);

	/**
	 * Visits an unknown kind of type. This can occur if the language evolves
	 * and new kinds of types are added to the {@code TypeMirror} hierarchy.
	 * 
	 * @param t
	 *            the type to visit
	 * @param p
	 *            a visitor-specified parameter
	 * @return a visitor-specified result
	 * @throws UnknownTypeException
	 *             a visitor implementation may optionally throw this exception
	 */
	R visitUnknown(TypeMirror t, P p);
}
